I am not speaking from experience here but if you leave the hops in too long you could get a grassy taste from it. Most people only recommend leaving the hops for dry hopping in for 10 to 14 days to avoid this.
If you are using hole hops i guess it could cause some pouring issues if it swells too large to get out of the bottle. Which you could probably work around but I would be concerned about grassy flavors.
I once read about the dangers of drinking, I have since stopped reading. - Unknown